Death on the Nile cause, perhaps (3)
I believe the answer is:
asp
'death on the nile cause perhaps' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asp that I've seen before include "Small poisonous snake" , "It proved deadly for Cleopatra" , "Kind of snake - what a sap" , "Joe Blake is Australian species" , "Slithery thing" .)